The invention relates to a conductive element and a method of making the conductive element. In particular, the invention relates to a conductive feedthrough for use in discharge lamps and a method of coating the conductive feedthrough.
Usually, discharge lamps consist of an outer envelope made of ceramic that encompasses an inner enclosure known as sealed envelope or “arc tube”. The sealed envelope is usually made of quartz, yttrium aluminum garnet, ytterbium aluminum garnet, micro grain polycrystalline alumina, polycrystalline alumina, sapphire, and yttria. The alumina or yttria based sealed envelope employs pure niobium or a niobium alloy as a conductive feedthrough material since niobium has a coefficient of thermal expansion compatible to that of yttria and alumina based ceramics. At high temperatures niobium has a very poor chemical resistance to oxygen and nitrogen, and the resistance substantially decreases as the temperature increases. As a result, the sealed envelope cannot be operated in air and has to be operated in a protective environment, which is typically a vacuum, or inert gas. Protective environment is provided by maintaining a vacuum or providing an inert gas in the space available between the outer envelope and the sealed envelope. The use of the outer envelope decreases the optical efficiency of the lamp. Further, the use of the outer envelope results in the size of the lamp being larger, and also adds to the cost of the lamp.
Accordingly, there exists a need to produce a conductive feedthrough having oxidation resistance and nitride formation resistance. What is also needed is a conductive feedthrough that can operate effectively in air at high temperature.